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D A Stubbs

Publications and source records attributed to D A Stubbs.

46 records · Page 3Linked to original sources
PubMed1976

Response bias and the discrimination of stimulus duration.

Pigeons discriminated stimulus duration in a psychophysical choice situation. Following presentation of any duration from a set of short duration (11 to 15 sec), responses on a red key were reinforced intermittently. Following presentation of any duration from a set of long durations (16 to 22 sec), responses on a green key were reinforced intermittently. Relative reinforcement rates were manipulated for choice responses across conditions. As relative reinforcement rates were varied, psychometric functions showed shifts in green-key responses at all durations. A signal-detection analysis showed that sensitivity remained roughly constant across conditions while response bias changed as a function of changes in relative reinforcement rate. Relative error rates tended to match relative reinforcement rates.

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PubMed1976

Scaling of stimulus duration by pigeons.

Pigeons were presented with a series of key-illumination time periods. During these periods two response keys were lit, one by white light and the other by red or green. White-key responses changed the color on the other key and green- and red-key responses intermittently produced food. Choice responses were reinforced at either of two intervals timed from the onset of the stimulus period. Food was scheduled for green responses during the shorter interval in some stimulus periods and food was scheduled for red-key responses at the longer interval during alternate stimulus periods. The temporal location of food in the stimulus periods was varied across conditions. Across conditions, the pigeons responded on the green key until the time at which green-key responses might be reinforced had passed; then, the probability of red-key responses increased as the time approached at which red-key responses might be reinforced. In all conditions, the pigeons, changed from green-key to red-key responses at the time that was an equal relative temporal distance from the two intervals where these responses were reinforced.

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PubMed1974

Concurrent performances: stimulus-control gradients during schedules of signalled and unsignalled concurrent reinforcement.

On one key, pigeons' pecks were reinforced according to a variable-interval schedule in the presence of vertical lines, and were not reinforced in the presence of oblique lines. On a second key, pecks were reinforced according to a variable-interval schedule in the presence of blue, according to a signalled variable-interval schedule in the presence of red, and were not reinforced in the presence of white. Subsequently, during extinction, stimulus-control gradients were obtained by presenting eight different line orientations on the first key concurrent with each of the three colors on the second key. On the first key, line-orientation gradients tended to be lower, narrower, and less shifted in peak or area when the second-key stimulus was blue or red, the stimuli respectively correlated with unsignalled and signalled reinforcement, than when it was white, the stimulus correlated with extinction. Thus, the effect on first-key line-orientation gradients depended on second-key stimuli correlated with concurrent reinforcement, whether or not these stimuli were also correlated with concurrent responding. As a function of first-key line orientation, an inverted gradient was obtained on the second key during blue; during both red and white, rates of pecking on the second key were near zero.

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PubMed1972

Second-order schedules: brief shock at the completion of each component.

Pigeons worked on second-order schedules in which completion of fixed-interval component schedules was reinforced with food according to a variable-interval schedule of reinforcement. The completion of each fixed-interval component resulted in the presentation of a brief electric shock. In one condition (shock-paired), the completion of every fixed-interval component, including those that ended in food, resulted in the shock. In another condition (shock-nonpaired), completion resulted in shock except for those components that ended in food. Shock presentations resulted in a positively accelerated rate within fixed-interval components. This patterning within components was similar whether the shock was intermittently paired with food or not. Response rates tended to decrease as shock intensity increased. The characteristic fixed-interval response pattern within components did not occur when shock presentations were omitted at the end of each component (tandem schedule). When shocks were scheduled but food was no longer presented (extinction) response rates declined to a near-zero level. The performance under shock conditions is similar to that in other studies in which visual and auditory stimuli are presented at the completion of component schedules.

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PubMed1972

Second-order schedules: comparison of different procedures for scheduling paired and nonpaired brief stimuli.

Pigeons performed on a second-order schedule in which fixed-interval components were maintained under a variable-interval schedule. Completion of each fixed-interval component resulted in a brief-stimulus presentation and/or food. The relation of the brief stimulus and food was varied across conditions. Under some conditions, the brief stimulus was never paired with food. Under other conditions, the brief stimulus was paired with food; three different pairing procedures were used: (a) a response produced the simultaneous onset of the stimulus and food; (b) a response produced the stimulus before food with the stimulus remaining on during food presentation; (c) a response produced the stimulus and the offset of the stimulus was simultaneous with the onset of the food cycle. The various pairing and nonpairing operations all produced similar effects on performance. Under all conditions, response rates were positively accelerated within fixed-interval components. Total response rates and Index of Curvature measures were similar across conditions. In one condition, a blackout was paired with food; with this different stimulus in effect, less curvature resulted. The results suggest that pairing of a stimulus is not a necessary condition for within-component patterning under some second-order schedules.

Journal Article↗
PubMed1971

Second-order schedules and the problem of conditioned reinforcement.

Thirteen pigeons were exposed to a variety of second-order schedules in which responding under a component schedule was reinforced according to a schedule of reinforcement. Under different conditions, completion of each component resulted in either (1) the brief presentation of a stimulus also present during reinforcement (pairing operation), (2) the brief presentation of a stimulus not present during reinforcement (nonpairing operation), or (3) no brief stimulus presentation (tandem). Brief-stimulus presentations engendered a pattern of responding within components similar to that engendered by food. Patterning was observed when fixed-interval and fixed-ratio components were maintained under fixed- and variable-ratio and fixed- and variable-interval schedules. There were no apparent differences in performance under pairing and nonpairing conditions in any study. The properties of the stimuli presented in brief-stimulus operations produced different effects on response patterning. In one study, similar effects on performance were found whether brief-stimulus presentations were response-produced or delivered independently of responding. Response patterning did not occur when the component schedule under which a nonpaired stimulus was produced occurred independently of the food schedule. The results suggest a reevaluation of the role of conditioned reinforcement in second-order schedule performance. The similarity of behavior under pairing and nonpairing operations is consistent with two hypotheses: (1) the major effect is due to the discriminative properties of the brief stimulus; (2) the scheduling operation under which the paired or nonpaired stimulus is presented can establish it as a reinforcer.

Journal Article↗
PubMed1969

Concurrent responding with fixed relative rate of reinforcement.

Responding by pigeons on one key of a two-key chamber alternated the color of the second key, on which responding produced food according to a variable-interval schedule of reinforcement. From time to time, reinforcement would be available for a response, but in the presence of a particular stimulus, either red or green light on the key. Red or green was chosen irregularly from reinforcement to reinforcement, so that a proportion of the total number of reinforcements could be specified for each color. Experimental manipulations involved variations of (1) the proportions for each color, (2) changeover delay, or, alternatively, (3) a fixed-ratio changeover requirement. The main findings were: (1) relative overall rates of responding and relative times in the presence of a key color approximated the proportions of reinforcements obtained in the presence of that color, while relative local rates of responding changed little; (2) changeover rate decreased as the proportions diverged from 0.50; (3) relative overall rate of responding and relative time remained constant as the changeover delay was increased from 2 to 32 sec, with reinforcement proportions for red and green of 0.75 and 0.25, but they increased above 0.90 when a fixed-ratio changeover of 20 responses replaced the changeover delay; (4) changeover rate decreased as the delay or fixed-ratio was increased.

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PubMedDate not supplied

Trunk stresses in construction and other industrial workers.

One of the problems arising from the consideration of safely during manual handling in industry has been, firstly, a definition of those workers at risk and, secondly, a definition of safely. To be able objectively to identify those a risk and quantify the stress to which they are exposed, a more rigorous series of criteria is required if prevention of back pain in industry is to be achieved. This paper concerns such a methodology which allows the quantification of truncal stresses to which identifiable high-risk industrial groups are exposed. The methodology is described using three industrial examples of populations who suffer considerable back hazard from their occupations. In the examples given, both direct measurements of truncal stresses will be presented together with contour applications whereby the safety of a handling task can be assessed by reference to diagrams.

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